1. Field of the Invention
The present invention relates to a novel wear-resistant polyoxymethylene resin composition and a process for producing it. More particularly, the present invention relates to a wear-resistant polyoxymethylene resin composition which especially has excellent wear resistance and is suitable as a material for the manufacture of precision machine parts, office automation devices and sliding automobile parts, and an efficient process for the production thereof.
2. Related Art
Hitherto, polyoxymethylene resins have been widely used for the manufacture of various machine parts and office automation devices. These resins are engineering resins having well-balanced mechanical properties and excellent wear resistance.
However, the inherent wear resistance of the polyoxymethylene resin material is not necessarily satisfactory for sliding parts and accordingly, their use is limited. Thus, improvement of wear resistance in this connection has been demanded.
Under these circumstances, various processes have been proposed for improving wear resistance of polyoxymethylene resin. For example, addition of 1,4-butanediol and fatty acid ester to polyoxymethylene resin (Japanese Patent Kokoku No. 55-23304) and addition of boric acid ester of fatty acid glycerine monoester (Japanese Patent Kokoku No. 57-15616) to polyoxymethylene have been proposed, but these processes do not sufficiently improve the wear resistance.
The following processes have been proposed for improvement of impact resistance of polyoxymmethylene resin. That is, a process of adding an olefin copolymer of an .alpha.-olefin and a glycidyl ester of .alpha.,.beta.-unsaturated acid to polyoxymethylene resin (Japanese Patent Kokai No. 59-64654), a process of adding a modified .alpha.-olefin polymer to polyoxymethylene resin (Japanese Patent Kokai No. 59-204652), and a process of coupling polyoxymethylene resin and a functional ethylene copolymer with an isocyanate compound (Japanese Patent Kokai No. 1-299813). However, the objectives of these processes are not directed toward the improvement of wear resistance and thus such improvement of wear resistance cannot be expected.
A process of adding polyolefin to polyoxymethylene resin has been proposed for improving Young's modulus (Japanese Patent Kokoku No. 42-19498), but the objective of this process also is not directed toward the improvement of wear resistance and furthermore, the process actually results in a deterioration of wear resistance.